SE520929C2 - Method and apparatus for controlling a braking system - Google Patents

Abstract

Proposed are a method and a device for controlling a braking system of a vehicle, braking force being maintained in at least one operating state at least one wheel of the vehicle while the braking pedal is actuated, independently of the degree of the pedal actuation. In this context, different conditions are provided jointly or alternatively for activating or deactivating the function.

Description

Vß 520 929 Advantages of the Invention.

An automatic parking brake or hill holder function, which maintains the braking force (locks the pressure) mainly when the brake pedal is sensed and sensed stationary, after the brake pedal is released the braking force is released again (preferably the function remains active for a certain time after the pedal is released, and after the time has elapsed or the starting request has been sensed (the braking force is resumed), a universally useful starting support follows, especially on uphill slopes. Advantageously, no roll-back of the vehicle occurs. The driver obtains a clearly reproducible behavior, in which release of the service brake in the medium term in each case leads to an unbraked vehicle, as he is used to even in vehicles without this additional electronic function.

In a particularly advantageous manner, therefore, misuse of the hillholder function as a parking brake is not possible.

It is further particularly advantageous that in the case of a hydraulic braking system only relatively low requirements need be placed on the pressure holding capacity of the valve which locks the brake piece. This is because the time during which the pressure difference prevails over the valve is limited.

It is particularly advantageous that it is ensured that the driver is prepared when the function is activated and thus in the event of a fault can take over the holding of the vehicle.

It is particularly advantageous that the hillholder function manages without extensive sensors, such as, for example, driver presence detection, and is universally useful, even with automated gearboxes.

Advantageously, the aforementioned requirements for activating and deactivating the hillholder function are supplemented by at least one additional requirement, which advantageously improves the ability of the hillholder to function. Advantageously, the determined length of time during which the maintenance of the braking force is extended with the actuated accelerator pedal and released brake pedal is extended, so that the vehicle is kept on uphill slopes for as long as the maintained braking force is required for starting.

In an advantageous manner, in a exemplary embodiment, a small braking force reduction resp. brake pressure reduction. The latter is also understood in the following as “maintaining the braking force” or “tensioning the braking pressure”.

Through the described conditions for activation resp. deactivation of the hillholdem is advantageously ensured that automatic holding of the vehicle only takes place when the driver is ready, ie. when the driver has not left the vehicle. This is also the case in connection with an automated gearbox, where clutch and / or gear information does not provide a report on the driver's presence.

Additional advantages appear from the following description of embodiments resp. of the dependent claims.

Drawing.

The invention is described in more detail below with the aid of embodiments shown in the drawing. Fig. 1 shows a control device for the braking system of a vehicle, while fi g. 2 and 3 as flow diagrams show the connections during activation resp. when deactivating the hillholdem or the automatic parking brake function. F ig. 4 finally clarifies the mode of operation using time diagrams.

Description of embodiments.

Fig. 1 shows a control device 10 for controlling the braking system of a vehicle.

This control device 10 comprises an input connector 12, at least one microcoder 14 and an output connector 16. The input connector, the microcoder and the output connector are connected to one another by a communication system 18 for mutual data exchange. To the input connection 12 come input lines from various measuring devices, which in a preferred embodiment are connected in a bus system, e.g. CAN. A first input line 20 leads from a brake pedal current switch 22 to the control unit 10 and transmits to it a brake pedal switch signal BLS. Input lines 24 to 27 connect the control unit 10 to wheel speed sensors 28 to 31, via which signals regarding the speeds of the vehicle wheels are input. In a preferred exemplary embodiment, there is at least one further input line 32, via which at least one of the following quantities is transmitted: A second brake pedal switch signal sBLS, which provides redundant information for brake pedal action; a master brake cylinder pressure DS representing measurement signal quantity; an influence quantity GAS from an accelerator pedal or from an engine control device provides information on whether the accelerator pedal is actuated or not; a switch signal HAS, which indicates that a parking brake is actuated; from a gearbox control a quantity GANG, which provides information about the engaged gear; from a motor control device a quantity M, which represents a measure of the motor torque, which is set or is to be set. Aggregates are set inside the control unit, which represent the status of a brake anti-lock control device ABS and / or a drive spin control device ASR and / or a travel dynamics control device ESP. Furthermore, in an advantageous exemplary embodiment, there is a further input line 36, which goes to the control unit 10 from a driver-actuated button switch 38, through the action of which the driver activates the hillholder function.

At the output coupling 16 of the control unit 10, output lines are arranged, which control actuating elements for controlling the wheel brakes of the vehicle. In a preferred embodiment, the brake system is a hydraulic brake system, so the output lines 40 lead to valves 42 for controlling the brake pressure in the individual wheel brakes, while via output lines 44 at least one pressure generating means 46 (pump) for the individual brake circuits is controlled. In a preferred embodiment, at least one control valve 48 is controlled via the outlet line 47, which in at least one wheel brake keeps the brake pressure constant when the brake pedal is actuated, in accordance with the described wheel rotation. In the preferred exemplary embodiment, this is at least one control valve, the switching valve intended for carrying out the drive spin control, which breaks the connection between the master brake cylinder and the wheel brakes. Instead of this valve, the brake pressure is also blocked by means of the valves which control the wheel brake pressure. The brake compressive stress takes place according to the design of all or only selected wheel brakes.

The present invention is not limited to use with a particular type of braking system. Thus, the solution in hydraulic braking systems with corresponding advantages can also be used in pneumatic braking systems or in connection with electrohydraulic, electromotive and / or electropneumatic braking systems. The braking force specified by the driver's brake pedal actuation, via conventional pressure lines or electrically by individual wheel brakes, is maintained at certain values or increased during active roller function during switching of valves and possibly pumps and / or constant control of control signals or switching of control signals. Especially in the case of electric motor braking systems, the electric motor-driven brake adjusting means for exerting a certain braking force is controlled by electric control signals, or is locked in a predetermined position.

In a preferred embodiment, the control device 10, more particularly the microcomputer 14, performs at least one drive spin control and possibly also a driving dynamics control under the control of the vehicle's braking system. Such regulations are known from the prior art. Furthermore, a so-called hillholder function, which in addition to a parking braking effect can also be used as a starting aid on a hill for manually shifted vehicles and lcryp underpressure for vehicles with automatic transmission. In such a hillholder function, the braking force (clamping force) specified by the driver is in principle maintained on a signal by means of a corresponding actuator control (especially the ASR switching valves) and lowered again under certain conditions. The demand signal for the hillholder function can for instance be derived from a pushbutton which can be actuated by the driver or from an automatic vehicle standstill, an example of which is known from the state of the art mentioned in the introduction.

The activation and / or deactivation of the automatic parking brake (hillholder) is derived from at least one of the approximate input quantities. The conditions mentioned below are utilized according to design either individually or in any combination.

Activation of the function occurs when the vehicle comes to a standstill (sensing via speed sensor or within an estimate as described in the prior art), the function is on standby (this is either always the case or only after a control switch has been actuated by the driver) and when the brake is trodden. In addition to these three main conditions, depending on the design, there may be at least one of the following conditions: The vehicle's drive motor must be in operation, which is determined by a corresponding, in the control unit memory fl agga or on the basis of an engine speed signal; the accelerator pedal is unaffected, which is determined by transmitting the corresponding information or transmitting a control variable for the accelerator pedal, which is compared with a predetermined minimum threshold value; a gear must be engaged, wherein in the preferred embodiment a corresponding fl agga is transmitted by a gearbox control; a master brake cylinder pressure above a certain threshold value must be present, the loaded master brake cylinder pressure being compared with the threshold value; the slope of the carriageway in the starting line must be positive, ie. the vehicle must start uphill, which is estimated on the basis of an inclination sensor and / or by means of other quantities; the parking brake is unaffected, which is sensed by the corresponding switch information.

The last condition prevents the abuse of hillholdem as a parking brake. If the driver e.g. only applies the parking brake slightly and leaves the vehicle, he observes, since the influence of the parking brake causes deactivation of the hillholdem (see below), that the vehicle can not be held by means of the effect of the parking brake.

When deactivating the hillholdem, the blocked pressure is reduced by partially or completely opening the pressure-locking valves in a beat-like, stepped or continuous manner. Correspondingly, the sustaining braking force is reduced by delivering corresponding control signals to the brake adjusting member. The deactivation takes place when at least one of the following conditions is present: a start request is sensed when the transmitted, motor torque representing the signal or engine speed exceeds a threshold value, whereby the measured or estimated information regarding the carriageway slope is included in the determination of the threshold value. to provide improved starting comfort, and when the coupling may not be opened; a certain length of time elapsed since the brake pedal was released; the vehicle speed is greater than a threshold value; the parking brake (or a foot-acting parking brake) is actuated, which in one embodiment is only taken into account after releasing the brake to avoid pedal repercussions; a certain length of time elapsed after a predetermined master brake cylinder pressure threshold value has been exceeded.

During deactivation, the length of time from releasing the brake pedal to the actual starting process is bridged and rolling back of the vehicle is prevented when starting uphill, as the braking force or the locked brake pressure is still maintained or reduced with a delay for a short time (approx. 1 second).

To further improve the starting process, it is envisaged to extend the holding pedal to extend the holding time when the starting wish is not present. In this case, the holding time after the brake pedal has been released must be extended (for example to 3 seconds).

The holding time after release of the brake pedal is determined with regard to a clear vehicle behavior, whereby disengagement must be impossible after the brake pedal has been released during active operation. In the event of a hesitant starting dry run, it is therefore not always ensured that this holding time is large enough to avoid rolling backwards. The holding time is extended if the accelerator pedal is depressed, so that the deactivation of the function takes place after a longer holding time if no start request is detected (the engine torque is still not sufficient).

As an alternative to these conditions for activating and deactivating the hill holder, there is also a transient passive coupling of the function, whereby a successive approach to an obstacle when driving downhill is facilitated. If the function were active in this condition, either gas must be given, which does not facilitate reaching the obstacle, or the time condition is waited out, which means poorer comfort. The passive connection of the system takes place preferably through a switch signal which can be actuated by the driver or when driving downhill (if by means of the sensed carriageway inclination).

In the preferred exemplary embodiment, the described methods take place as programs of the computer unit 14 and the control unit 10. An example of such a program is shown in fi g. 2 and 3 as flow diagrams regarding activation and deactivation of the function.

Fig. 2 shows the procedure for activating the hillholder function. The activation signal is generated by means of an and-connection 100 and is output as an output signal via a line 102 for closing a valve or an alternative adjusting element. The input signals to and from the connection 100 are formed as described below: The master brake cylinder pressure signal DS is ironed into a comparator 104 with a threshold value representing an actuated brake pedal, and an output signal is emitted when the signal exceeds this threshold value. This output signal is applied to an and-connection 106. In a comparator 108, the brake pedal switch seal BLS is compared with the value 1, which it exhibits when the brake pedal is actuated. This output signal is also applied to the and connection 106. Correspondingly, in a comparator 110 the signal from the safety brake pedal switch sBLS is compared with the value 1 and a signal is emitted when it has the value 1 (affected pedal) and is applied to the and connection 106. The output signal from and the connection 106 forms an input signal to the and connection 100.

A handbrake switch sigral HAS is ironed in a comparator 112 with the value zero. This value occurs when the parking brake is unaffected. If the signal has a value of zero, an output signal is sent to the and-connection 100. Furthermore, a gas pedal actuation quantity GAS is supplied and ironed in a threshold value step 114 with a predetermined threshold value, at the underside of which a released accelerator pedal is determined.

If so, an output signal is sent to the and-connection 100. Furthermore, in an estimation step 116, the vehicle speed VF is estimated, for example, on the basis of wheel speeds 10 5 20 929 9 VRAD as described in the prior art mentioned in the introduction. The vehicle speed VF is compared in a threshold step 118 with a minimum value, the underside of which indicates a stationary vehicle. If so, an output signal is generated as the input signal for the and connection 100. Furthermore, in the comparator 120, a gear information transmitted by a gearbox controller GAN G is compared with the value 1. This value represents a loaded gear. If this value is present, an output signal is sent to the and connection 100. Furthermore, the status fl ags are set aside in a memory element 122. A first status fl agga MOT indicates whether the vehicle's drive unit is running. In the comparator 124 this fl is compared with the value 1. If this is present (the motor is running) an output signal is given to the and connection 100. Furthermore, there are status fl units for the ABS and ASR function, possibly also for the ESP function, which have zero if the corresponding function is not active. Correspondingly, in the comparators 126 and 128 the status fl units are compared with the value zero. If both of these or units have the value zero (and the connection 130), an output signal is transmitted to the and connection 100.

The latter forms an output signal for activating the brake pressure barrier if input quantities are present at all inputs, ie. when all the mentioned conditions are met. The reproduction in fi g. 2 shows a preferred embodiment. In other embodiments, as stated above, activation conditions are used in other, arbitrary combinations with each other.

Correspondingly, the automatic parking brake is deactivated.

A corresponding flow chart is shown in fi g. 3, in which case deactivation generally takes place in the absence of any of the conditions.

The central element of this flow chart is an or-connection 200, which sends via the line 202 an output signal deactivating the brake pressure lock when an input signal is present on at least one of its inputs. A first input signal is formed in the or-connection 204 when one of the status fl readings from the memory 122 for the anti-blocking control device and the drive spin control device has the value 1 (see comparator 206, 208). A second input quantity is formed by means of an and-connection 210, this input quantity representing the driver's starting wish. This is formed when the accelerator pedal actuation quantity exceeds a predetermined threshold value (threshold value step 212), a switching signal KUP represents an unopened clutch (comparator 214) and a torque representing value of the drive unit MSOLL exceeds a predetermined threshold value 21 (threshold step 21). A third input signal is formed when the vehicle speed VF exceeds a predetermined threshold value (threshold step 218). A fourth input signal to the or-connection 200 is formed when the master brake cylinder pressure DS falls below a predetermined threshold value (threshold value step 220) and this threshold value is exceeded for a predetermined time length T1 (delay step 222). A fifth input signal to the or connection 200 is formed when either the brake pedal switch BLS or the safety switch sBLS represents an unaffected pedal (the value in each case zero, see comparators 224, 226 and or node 228), and a certain time T2 elapsed after sensing a slip. pedal based on at least one of these switch signals (delay step 230). The time length T1 is less than the time length T2. In this case, the time duration T2 of the delay stage 230 is extended if the actuation of the accelerator pedal is sensed in the threshold stage 212. A last input signal is formed through the connection 232 if one of the brake pedal switch signals (preferably the signal sBLS) indicates released brake pedal 23 and hand-held brake pedal no gear is engaged (compare comparator 236 and or node 23 8). If one of the input quantities is present at the or connection 200, the brake pressure lock is released.

An illustration of the mode of operation of the mode of operation shown is given by means of the time diagrams in fi g. Fig. 4a shows the time course of the vehicle speed, fi g. 4b for the brake pedal switch signal, fi g. 4c for accelerator pedal status (affected, unaffected) and fi g. 4d for status of the Switching Valve (open, closed). At time T0, the driver acts on the brake pedal (see fi g. 4b) and releases the accelerator pedal (fi g. 4c). The switching valve is open at this time (fi g. 4b). Until the time T1 520 929 11 T1 the vehicle speed decreases, whereby at the time T1 stationary of the vehicle is sensed. This results in affected brake pedal and released accelerator pedal according to fi g. 4d for control of the switching valve (fi g. 4d). The brake pressure is blocked. At time T2 the driver releases the brake pedal to be able to start (fi g. 4b), and at time T3 he acts on the accelerator pedal (fi g. 4c). If the accelerator pedal is unaffected at time T4 (predetermined time from T3), this would lead to the opening of the switching valve. This time is extended by the actuated accelerator pedal so that only at time T5 is the switching valve opened (fi g. 4d). Thus, the start is supported according to fi g. 4a even in the event of a hesitant start race, ie. without a start process being detected.

The above conditions for activating and / or deactivating the hillholder function are used according to the design example individually or in any combination.

Claims (6)

10 15 20 25 30 520 929 12 Patent claims A method for controlling the braking system of a vehicle, wherein in at least one operating condition with the braking pedal actuated braking force is maintained at at least one vehicle wheel regardless of the size of the pedal action, in the present case at least one condition the braking shaft is lowered again, characterized in that the first braking force time is reduced when the brake is released, and / or that the braking force is lowered after a second fixed time when after release of the brake the accelerator pedal is affected and / or that the braking force is reduced if, preferably when the brake is released, a parking brake is affected, and / or that the braking force is reduced when, after the master brake cylinder pressure falls below a predetermined threshold value, a predetermined time has elapsed, and / or the braking force is reduced when an anti-lock control device, a drive spin control device or a driving dynamics control device is active, and / or the braking force is reduced if no gear is engaged . Method according to Claim 1, characterized in that the braking force is reduced immediately when the condition in question occurs. Method according to claim 1, characterized in that the braking force is reduced when a starting request is sensed on the basis of accelerator pedal power, clutch status, engine torque and / or engine speed, possibly taking into account the carriageway slope, and / or when the speed exceeds a minimum value. A method of controlling the braking system of a vehicle, wherein in at least one operating condition under actuated brake pedal braking force is maintained at at least one vehicle wheel independent of the size of the pedal action, the braking force being reduced again when at least one condition is present, characterized in that the following conditions are present: A gear is engaged, a gear control regulator, an anti-lock control device, a driving dynamics control device is inactive, the vehicle's drive unit is running, a parking brake is unaffected, the carriageway inclination in the starting direction is positive, the accelerator pedal is unaffected. 5. Device for controlling the braking system of a vehicle, with a control unit which, in at least one operating condition under actuated brake pedal, emits at least one output signal which maintains the braking force at at least one vehicle wheel regardless of the magnitude of the pedal action, and which again reduces the braking force when at least one condition exists, characterized in that the control unit generates the braking force reducing signal after a first determined time, if the brake is released, and / or after a second determined time, if within the first time after release of the brake the accelerator pedal is actuated and / or if, preferably at release of the brake, a parking brake is affected, and / or if a predetermined time has elapsed after the main brake cylinder head has fallen below a predetermined threshold value, and / or if an anti-lock control device, a drive spin control device or a driving dynamics control device is active, and / or if no gear is engaged when the brake pedal is released. Device for controlling the braking system of a vehicle, with a control unit which, in at least one operating state under the actuated brake pedal, emits at least one output signal which maintains the braking force at at least one vehicle wheel regardless of the magnitude of the pedal action, and which again reduces the braking force when at least one condition exists, characterized in that the control unit emits the braking force holding the output signal, if at least one of the following conditions is present: A gear is engaged, a drive spin control device, an anti-lock control device, a driving dynamics control device is inactive, the vehicle drive is running, a parking brake is unaffected, in the starting direction is positive, the accelerator pedal is unaffected.